Studies on the effects of nitrendipine on oxytocin‐angiotensin II‐ and ergometrine‐induced contraction of pregnant human myometrium in vitro

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Abstract
Calcium channel blockers inhibit myometrial contractility by preventing the increase in intracellular free calcium which follows stimulation. They could thus be useful in treating premature labour. The effect of nitrendipine, a dihydropyridine calcium channel antagonist, on the contractile response of strips of pregnant human myometrium to oxytocin, angiotensin II (AII) and ergometrine has been examined. A total of 68 tissue strips were studied, with random allocation to treatment group. Initial concentration: response curves to one of the three agonists were determined; the concentration:response determinations were repeated in the presence or absence of nitrendipine at 10(-9)M. The initial EC50S for tissues exposed to oxytocin and AII were 8.2 X 10(-10)M and 3.4 X 10(-8)M respectively. The contractile response to both agonists was significantly blunted in the presence of nitrendipine (ANOVA; P less than 0.001 for both agents). This effect was greatest at high agonist concentrations. The initial EC50S for tissues exposed to ergometrine was 3.9 X 10(-8)M. Exposure to nitrendipine blunted the response (ANOVA; P less than 0.001), an effect most marked at low concentrations of ergometrine. The effect of nitrendipine on myometrial responses to the naturally occurring hormones oxytocin and AII supports suggestions of a role for it in inhibiting premature labour.